This application pertains to the art of spreaders for lifting containers and, more particularly, to such spreaders which are removably mountable upon the tines of a fork truck or the like.
Spreader frames for lifting containers are commonly mounted on tines of fork trucks or the like. The spreader frame has container engaging devices adjacent the corners thereof for latching onto cooperating latching devices adjacent the four upper corners of the container. Alignment of the container engaging devices on the spreader frame with the cooperating latching devices on the container is very difficult and often requires extensive manipulation of the vehicle by the operator. Once the container has been lifted and transferred to another place, further extensive manipulation of the vehicle is often required for properly aligning the container to stack same in a desired position.
Many arrangements have been proposed for overcoming the alignment difficulty. Prior patents related to such arrangements include Fitch U.S. Pat. No. 2,063,915 who discloses a traveling crane having a generally rectangular frame and pairs of rotatable hoisting drums. One pair of hoisting drums is mounted on a subframe for movement relative to the main frame. Movement of the one subframe places the drums generally at the corners of a rhomboid and this is not suitable for a spreader-type of container lifting device. Meister U.S. Pat. No. 3,176,866 and Levitt U.S. Pat. No. 3,387,730 disclose container lifting devices attached to fork-type of vehicles. A special construction allows transverse movement of the container lifting device relative to the vehicle mast. Green U.S. Pat. No. 3,552,,557 discloses a spreader frame mounted on fork tines for movement rotatably about a generally vertical axis, and horizontally in directions both transversely and longitudinally of the fork tines. While this arrangement includes all of the desired movements for properly aligning the spreader frame with the top of a container, rotatable movement is accomplished by angularly shifting box beams relative to the fork tines. This means that the box beams must be extremely wide in order to accomplish the desired rotational movement and the necessary width of the box beams makes it possible to have transverse misalignment of the base frame relative to the tines so that the load supported on the spreader frame would be unbalanced. In addition, Green connects hydraulic cylinders directly to the horizontal portions of the fork tines and this requires modification of such tines by drilling holes therein. In addition, the spreader is not selfcontained for performing the alignment movements and connection of power cylinders to the fork tines is required. This makes mounting and dismounting of the spreader frame relative to the tines more difficult. Rumell U.S. Pat. No. 3,688,933 discloses a spreader frame mounted on fork tines for movement rotatably, and horizontally in directions both transversely and longitudinally of the tines. There is no provision for power movement of the Rumell spreader frame relative to the tines and this makes it difficult to align such frame. Kinross U.S. Pat. No. 3,709,392 discloses a spreader frame similar to Green and includes a special mounting arrangement for horizontal transverse movement of the frame. Tredray U.S. Pat. No. 3,713,556 is also similar to Green and further includes an arrangement for extending the container engaging devices for placing them at the corners of different size rectangles in order that the spreader frame can be used to lift containers of different sizes.